In recent years, the technique for increasing output and intensity of a solid-state laser unit has been developed and a solid-state laser unit satisfying both of the performances has been realized. Consequently, precise welding and micro removing process which could not be realized by conventional processors can be performed very precisely at high speed. A high-output high-intensity solid-state laser unit has come to be actively used for spot welding and seam welding process for electric and electronic parts and for scribing and cutting process for metals, semiconductors, ceramics, and the like.
As a representative example of a conventional solid-state laser unit, FIG. 3 shows the configuration of an LD (Laser Diode)-pumped pulse type Nd:YAG laser system whose laser active medium is a rod type Nd:YAG crystal and whose average output is 300 W class which is most spread in the markets.
An Nd:YAG crystal 1 is pumped by LD beams 3 emitted from LDs 2 as a pumping source. Light of 1.06 μm emitted from the Nd:YAG crystal 1 is selectively amplified between a total reflection mirror 5 and an output coupling mirror 6 constructing a laser resonator 4. The amplified light goes out as an Nd:YAG laser beam 7 from the output coupling mirror 6. A control on the Nd:YAG laser output according to use is performed by a DC stabilizing power source 8 which is electrically coupled to the LDs 2. To maintain a stable Nd:YAG laser output, the temperatures of the Nd:YAG crystal 1 and the LDs 2 are controlled directly or via a cooling medium supplied from a cooling medium supplying apparatus 9 so that the temperatures of the peripheral parts become constant.
The Nd:YAG laser beam 7 is condensed by an incident light condensing optical system 10 so as to satisfy transfer conditions of an optical fiber 11 for transmission having a core diameter of 0.3 mm. The laser beam emitted from the optical fiber 11 is shaped or condensed by an outgoing light condensing optical system 14 so as to have a beam shape adapted to processing on a workpiece 13 placed on a CNC table 12, and desired laser processing is performed.
In the conventional configuration, however, energy conversion efficiency (hereinbelow, called “electricity-light conversion efficiency”) of a laser beam emitted from the laser system from the electric energy input to the LD for pumping in the case of performing laser processing is a very low value which is about 10 to 20%. A breakdown of the value is that electricity-light conversion efficiency of the LD for pumping is 30 to 50%, and energy conversion efficiency from the energy of LD-pumped light to an Nd/YAG laser beam (hereinbelow, called “light-light conversion efficiency”) is 35 to 50%. The “electricity-light conversion efficiency” is the product of the “electricity-light conversion efficiency of LD” and “light-light conversion efficiency”.
Further, as shown in FIG. 4, the energy absorptance with respect to laser beams of general industrial materials of aluminum (hereinbelow, expressed as “Al”), copper (hereinbelow, expressed as “Cu”), and iron (hereinbelow, expressed as “Fe”) is about 5%, 2%, and 36%, respectively, at an oscillation wavelength of 1.06 μm of an Nd:YAG laser beam (the source: J. H. Weaver, “Physics Data—Optical Properties of Metal”).
Accordingly, the ratio of energy absorbed by a workpiece in the electric energy which is actually input to an LD is lower. The energy ratio is very low and is 0.5 to 1% in the case of Al, and 3.5 to 7% even in the case of Fe having high absorptance.
Although a laser processor on which a conventional solid-state laser unit is mounted can obtain high-speed high-precision processing performance, it has a problem such that, due to the very low ratio of energy utilization, the introduction and operation costs of a laser system are high. All of the remaining energy which is not shifted or converted to the final Nd:YAG laser beam becomes heat by which a cooling medium for cooling the LDs and the Nd:YAG crystal is heated. As a result, the heat is exhausted from the cooling apparatus to the periphery. Although the laser is clean, a secondary problem such that the laser emits heat to the peripheral environment occurs.
In consideration of such a problem, an attempt to use an LD beam having electricity-light conversion efficiency of 40% or higher directly for processing has been made. However, the condensability of the LD light is low and it is difficult to transmit an output of a 300 W class necessary for use in general processing via an optical fiber having a small diameter of 0.3 mm or less.
The present invention provides a laser system which solves problems of high cost and high power consumption of the laser system due to low energy conversion efficiency, which are problems in a high-output high-intensity solid-state laser unit.